Implantable medical devices (IMDs) and external medical devices (e.g., wearable devices, insertable cardiac monitors, implantable pacemakers, or implantable cardioverter-defibrillators) may record cardiac electrogram (EGM) signals for sensing cardiac events such as P-waves and R-waves. IMDs may detect episodes of bradycardia, tachycardia, or fibrillation from the sensed cardiac events, and respond to the episodes as needed with pacing therapy or high-voltage anti-tachyarrhythmia shocks (e.g., cardioversion or defibrillation shocks). Some IMDs include, or are or part of a system that includes, sensors that generate other physiological signals, such as signals that vary based on patient movement or activity, cardiovascular pressure, blood oxygen saturation, edema, or thoracic impedance. Physiological parameters determined based on such signals may be used to assist in the detection of arrhythmia, as well as the detection or monitoring of other cardiac conditions, such as heart failure or infarction. Delivery of therapy in response to detection of a cardiac event, such as ventricular tachyarrhythmia, may negatively impact a patient's quality of life, while delayed treatment may present risk to the patient.